Extrusion method and apparatus



Dec. 9, 1952 M. W. OLSON EXTRUSION METHOD AND APPARATUS 2 SHEETS-SHEET l Filed Feb. 16, 1949 A 1. 4; 7274 vv.. lWf\.\\\\\\.w///\\\\m De@ 9, 1952 M. w. oLsoN 2,620,515

' ExTRusIoN METHOD AND APPARATUS Filed Feb. 1e, 1949 2 SHEETS-SHEET 2 Arralw'r Patented Dec. 9, 1952 EXTRUSION METHOD AND APPARATUS Mark W. Olson, Allendale, N. J., assigner to United States Rubber Company, New York, N. Y., a corporation of New Jersey Application February 16, 1949, Serial No. 76,799

15 Claims.

This invention relates to a method and apparatus for the extrusion of rubber and other exrtrudable materials. More particularly, thisl invention relates toa method and means for extruding continuous lengths of hollow articles suc as rubber tubingA and the like.

One object of the invention is to provide a method and apparatus for the continuous eX- trusion of rubber hose or other tubular articles having smooth shiny surfaces free from blemishes,V and in which the rubber has been conned to provide a dense homogeneous compound.

Another object of the invention is to provide a method and apparatus for shaping extrudable material into continuous lengths of articles having a hollow longitudinal cavity which is accurately centered with respect to the Walls of the article.

A further object is the provision of a method and means for manufacturing rubber tubing, or the like, of various wall thicknesses.

It is another object of the invention to manufacture lengths of hollow articles from rubber or other materials by a method and apparatus capable, by simple adjustment, of producing articles of various wall thicknesses.

Still another object is the provision of an improved extruding mechanism for manufacturing continuous lengths of hollow articles from vulcanizable materials having means -for vulcanizng the materialduring the extrusion, and which is capable of extruding various hollow articlesy in long lengths without jamming, tearing, or damage to the vulcanized stock.V

It is also an object of the invention to manufacture plastic articles having a generally annular cross-section by extruding or forcing the plastic along a conning passageway, the pas-l sageway being lubricated to facilitate movement of the plastic without tearing or rupture or functional distortion.

Still a further object is to provide a method and apparatus-for 'extruding lengths of shaped plastic articles having a longitudinal hollow cavity, by forming the desired cavity in the material While passing the material in a plastic, readilydeformable state through a confining passageway, and thereafter causing the material in the coniining passageway to change to a relatively nonplastic state in which it is capable of retaining its shape. l

Another object of the invention is to shape continuous lengths of hollow articles from plastic material'by the agency of Viiuid pressure acting within the plastic material.

An extrusion apparatus constructed according to the present invention and adapted 'to Aillustrate the practice of the method of the invention is shown in the accompanying drawings, wherein:

Fig. 1 is a longitudinal section of an extruding apparatus for shaping and vulcanizing rubber tubing in an elongated lubricated confining tube in accordance with the present invention;

Fig. 2 is a similar view on a larger scale of part of the apparatus of Fig. l;

Fig. 3 is a cross-sectional view of the apparatus taken along the line 3-3 of Fig. 2;

Fig. 4 is a cross-sectional View taken along the line 4-4 of Fig. 1;

Fig. 5 is a. view, partly in section, showing the exit end of the confining tube in full;

Fig. 6 is a cross-sectional view taken substantially along the line 6-6 of Fig. 1;

Fig. 7 is a sectional view of part of the apparatus taken along the line 1 -l' of Fig. 6, and

Fig. 8 is a detailed view of part of the means for lubricating the elongated confining tube.

Broadly, the method of the present invention comprises a process for manufacturing tubing or other hollow articles from rubber or similar extrudable material, wherein the desired hollow or cavity within the article is created through the agency of uid pressure exerted by a body of iiuid within the material while it is being extruded in the plastic state. The method is further characterized by the fact that the said uid pressure is exerted on the plastic material While it is being extruded thro-ugh an elongated confining or shaping chamber. The plastic material lls out and conforms to the walls of the elongated chamber, and the wall of the chamber is supplied with lubricant, so that the plastic material advances along the chamber without sticking or tearing and the resulting. article has a smooth shiny surface free from blemishes. If the article is being made from vulcanizable material, the said conning chamber is heated to effect vulcanization of the material before it issues from the confining chamber. Since the material in the chamber is under pressure, a dense, compacted, vulcanized article of good physical properties obtained. If the article isv being made from a material of thermoplastic nature, the chamber is equipped with suitable cooling means so that the material is cooled sufficiently to be in a relatively non-plastic, shape-retaining state on issuing from the conining chamber.

As shown in'the accompanying drawings, suitable apparatus forl rcarrying out themethod of the invention includes an elongated die extension a simple adjustment to be described in detailVv below. Thus, tubes of a variety of wall thicknesses can be manufactured in the saine apparatus. This is in contrast to conventional tube manufacturing apparatus, 'wherein the wall oiv the tube is shaped .by an annular die, adifferent' size of die being required for each desired Wall thickness. The tubing made in this apparatus is accurately centered and of exceptionally uniform wall thickness.

Turning now to the details :of construction and referring-to Figs. l, 2 and 3 of the drawing, the apparatus for shaping and vulcanizingtubing,

or the like, comprises a conventional extruder I0 having a feeding screw I I which is rotated within a-barrel or cylinder I2 by any suitable drivev means (not shown). In order ,to maintain the vulcanizable rubber compound I3 being extruded at the proper working temperature, the extruder body I9 may be heated by any conventional means such as steam. Rotation of the -screw II causes the heated plastic .rubber stock I3, which is initially in a shapeless condition, to `be forced along the barrel I2, through openings I4 in a spider ring assembly I5, andthence through a die member I3 into -an elongated die extension tube, or conning jchamber'H, in which the rubber stock I3 is shaped andvulcanized under pressure. The rubber stock I3fills the die extension tube I1, and conforms to the walls thereof, because there is provided at the exit end of the tube I1 a restricting or snubbing device, to be described below, that permits the extruder feeding screw II to develop considerable backpres'sure on the rubber stock within the tube.

n 'In orderrto makeY possible the passagey of the rubber stock I3V under` pressure through the long die extension tube I1., which mayv berof great` length, e s-lfio @fester @Vee cloni-*Germans is provided vvfor continuously applying -a thin lm or lubricant to Athe surface of ythe advancing rubber stock as it enters the tube I1. to preventI sticking of the rubber to the interiorwall thereof. This means includes a lubricant applying ring I8', which is shown lin Fig.. B'reinovedffrbm the apparatus, and which has a number of tapered blades I9 extendingvoutwardly therefrom. The blades are separatedb'y slots 20. This lubricating ring assembly serves tov spread lub'r'ica'nt introduced under pressure, evenly Aover the surface of the passing rubber stock I3. and also serves to prevent the rubber from entering into and clogging the lubricant supply passages.

The lubricating ring I8 is held, against the. forward face of the die lI6 by a collar 2I'a'ttached a smooth continuous passage from the 'die I6 to the interior of the tube I1.

The iubificam t9 be applied tothe rubberv surface is supplied from a reservoir 2B by a variable speed positive pump 21, driven by a, motor 28. The lubricant may be any suitable liquid which has anti-sticking properties and which is not deleterious to the rubber, such as silicone mold release fluid. A lubricant line 29 of fine bore connects the pump 21 with a passagewayiS within theco1lar2l on the tube I1. A gauge 3l on the line 29 vindicates the pressure of the lubricant. The lubricant passes from the passageway 30 into an annular distributing passageway` 32V (Figs. 2 and 3) from which a series of radial holes33 lead through the wall of the tube I1 tothe lubricating ring blades I9. As the'lubricant is `forced under positive pressure `by the pump l21 through these passageways, the blades-I9 ilex slightly away from the openings 33 and serve Vto distribute a thin lm of lubricant evenly over the surface of the passing rubber I3. At the same time the blades I9, which are thin enough tonex somewhat under a relatively slight pressure diierential, are capable of nexing against the radial lubricant openings 33, closing them on and preventing any of the rubber stock I3 from entering therein in the event that the pressure of the rubber stock exceeds the pressure of the lubricant. This action of the lubricating ring prevents breakdown of the lubricated extrusion operation due to clogging of the lubricant entrances 33 with rubber particles.4 Lubricated extrusion apparatus of this character is claimedin the copending application of the present inventor and C. -A. Ferguson, Serial No. 61,654, filed-November '23, 1948, and assigned to the same assignee as the instant application.

In order to eiect vulcanization of the rubber) stock I3 as it passes through the tube I1, the tube may be heated by virtue of its own electrical resistance to current introduced at terminals 34 and35 at each endof thetube. The tube may` be covered with suitable heat insulation 36.

For the purposeofshaping the plasticv rubber mass I3 within the tube I1 into the desired form, namely, that of a hollow rubber tube 31., by fluid pressure-in the manner of this invention, means are provided for introducing al finecontinuous stream 38 ovfhuid. at thecentral axis of the advancing rubber mass I3. For purposes of 'illustration, the. nuidA is hereinafter represented as being a-liquid. This stream-of liquid 38 is int-roduced-througha hollow vneedle 39, which extends forwardlyfrom the spider ring assembly I 5. The spider ring assembly, .whichts `into a recessed portion of the extruder head-24, consists of an outer ring 40, land a numberuof spokes 4I which support a central hub 42. The centralhub 42 has a forwardly tapered portion v43 extending intothef'die I6 on the central axis thereof., and the Vhollow needle 39v extends a Ashort Vdistance into the confining tube -I1 from this tapered portion 43.

In-order to feed a suitable shaping liquid, for example, glycerine, contained in a reservoir 44,. through the hollow Vneedle 39,- there 4isf-provided a variable 4speed pump 45, driven by asuitable motor 45. This pump -isuof thepositive delivery type, such as a gear pump, .andinay be rcritically adjusted to deliver the desired quantity offliquid-at the desired pressure The pressure is indi-- cated on a pressure gage:41 ina connecting line` 48, leading from the pump 45 to a passageway 49 through the spider spoke 4I and the spider hub'4'2. v

As the rubbergstock I3 advances from. the entrance end of the elongated conning chamber or tube I1 toward the exit end thereof, it is heated to a higher temperature and becomes highly plastic before vulcanization takes place. The stock I3 while in rthis highly plastic state is shaped into the desired `tubular for-m by the pressure of a body of the liquid introduced into the stock. For this purpose, restricting means is provided, at the exit end of the tube I1, for causing the ne stream of liquid 38, introduced, as explained previously, through the hollow needle 39 at the central axis of the advancing rubber mass, to accumulate within the soft plastic mass of rubber, forming an enlarged bubble 53, which progressively enlarges the interior cavity .and thus shapes the rubber mass I3 into the form of a tube 31. The rubber is in its most plastic and easily deformable state at a section of the tube just prior -to the area where appreciable Vulcanization sets in, and it is Aat such section of the tube that the body of uid achievesl its maximum diameter. In other words, the liquid bubble forms, in effect, a liquid mandrel supporting the interior of the tube. The liquid bubble 53 and the rubber tube 31 are shown in cross-section within the conning tube I1 in Fig. 4. Suitable restricting means for causing the enlarged bubble 53 to form comprises a pair of driven pinch rolls 54 and 55 which collapse and compress thevulcanized rubber -tube 31 as it emerges from the confining tube I1, thereby limiting the flow of liquid from the interior ofV the plastic rubber mass I3. In this way, the bubble 53 accumulates atthe softest part o-f the plastic mass I3, and develops sufcient hydraulic pressure, by the action ofthe pump 45, to shape shape by reason of its own elasticity immediately after passing from the pinch rolls, as shown in Fig'. 1.

In order to drive the pinch rolls 5d and 55 a thedesired speed, there is provided a motor 60 and a variable speed transmission 6I which is connected by a driving shaft E2 to a gear box assembly 63. As shown in Fig. 6, the rotation of the driving shaft 62 is transmitted to the upper pinch roll 54 through bevel gears 64 and 65, and upper roll shaft 66. In order to drive the lower pinch r-oll 55 at the s-ame speed as, and in the vopposite direction' to the upper roll 54, there is provided in the gear -box l63 a train of gears 61,68, 69, and 10, which rotate in the directions indicated by the arrows in Fig. '1. The gear 61 on the upper pinch roll shaft 66 drives the idler gears 68 and 69 on shafts 1I and 12 respectively, and the gear 69, in turn, drives the gear 10 on lower pinch roll shaft 13.

By adjusting the variable speed transmission 6I, the speed of thepinch rolls 54 and 55 can be regulated. These pinch rolls grip the vulcanized rubber tube 3 1 tightly, and thev speed of the rollsdetermines the rate at which the rubber 'tube passes'from the confining and vul# canzing tube I1. This regulation of the speed of 'emergencerof the rubber tube 31 affords a means of varying at will the wall thickness of the 'rubber'tubing .being produced` The reasonI 6. why this is possible will be understood from consideration of the fact that, under steady operating conditions, the volumetric rate of' ow of rubber into the confining tube I1 is necessarily the same as the volumetric rate of flow of rubber out of the tube. Hence, for a given constant rate of. introduction of vulcanizable stock into the confining tube, the wall thickness of the vulcanized product 31 will vary inversely wi-th the linear speed at which the product is withdrawn from the confining tube. Thus, if the product 31 is permitted to emerge at a Very much faster rate than the rate at which stock I3 is introduced into the tube I'I, then the product will have a thin wall; as the speed of emergence is decreased, the wall of the product becomes thicker. Thus, the present extrusion method and apparatus permit easy adjustment of the wall thickness of the extruded vulcanized tubing. In this way tubing` of a variety of wall thicknesses can be manufactured in ythe one apparatus, thereby simplifying factory operations and effecting economies in production.

When a centrally located liquid bubble 53 is used to shape the tubing in the manner of this invention in place of a solid core or mandrel within a die passageway in the conventional manner, the passage within the tubing is accurately centered. By this method the problem of maintaining a long solid core or mandrel in proper concentricity with the outer tube I1 is avoided, and wastage of material due to improperly formed tubing is minimized, y

Under steady operating conditions, the rate of introduction of the liquid stream 33 by the pump I5 is such as to just replace the small amount of liquid which escapes through the compressed rubber tube 31 as .it passes between the pinch rolls. The desired hydraulic shaping pressure in the liquid body 53, within the rubber mass, is maintained by the squeezing action of the pinch rolls 5@ and 55. 'Ihis pressure may bernaintained at a desired level, by adjusting the` pressure exerted by the pinch rolls. To this end, thershaft 'f3 of the lower pinch roll 55 is made adjustable with respectl to the shaft 66 of the upper pinch roll 54, sov that the distance betweenthe two rolls may be varied as desired.

A convenient way of accomplishing this is indicated in Figs. 6 and '1 wherein the lowerv pinch roll shaft 13 is shown rotatably supported on .two arms 14 and 15 which are pivotally mounted on the lower idler gear shaft 12,. and which are rigidly connected by a crosspiece 16, the entire assembly forming a pivoted yoke. The vposition of the pivoted yoke, and hence of the roll shaft 13, may be critically adjusted` by means of an adjusting screw 11 which is threaded through the wall of the gear box at 18. The roll shaft 13 is spring loaded by a compression spring `13v fixed to the wall of the gear box 63 at one end and fixed to the yoke crosspiece16 at the other end. The spring 13 and the adjusting' screw ..11 t into a recessed portion 8B of the crosspiece 1S.

After passing from the pinch rolls, the vulcanized rubber tube 31 may be cut into convenient lengths, and the small amount of liquid which passes through the nip of the pinch rolls` may be permitted todrain out of the tubing, or it may bewashed out, before the tubing is packaged for sale.

.The lubricant introduced between the outer surfaceof the advancing rubber mass I3 and the inner walls of the conning tube I 1 vby the lubricant pump.21 is-permitted to pass out-at the exit endof the tube I1. The amountof'lubricant which is thus-passed through the tube I1 is very small, since only a thin film of lubricant isdesired betweenthetube and the advancing rubber. The surfaces ofthe pinch rolls 54 and 55 `are preferably knurled or ridged so that the lubicant will not tend to cause the-'rubber vtube 31 to slip between thorens, which would destroy thecontrolling effect of the speed ofthe rolls on the rate-of Yemergence -of the rubber product. The pinch rolls therefore grip 'the rubber-product rmly as it emerges fom the conning tube, and thereby limit the speed of emergence of the prod-'- uct `from the conning tube.

AV method of starting and operating the appa ratus will now be-described. As the 1 vulcanizable rubber stockr I3 is started into the confining tube I1 by the stuffer screw II,l the variable speedlubricant pump 21 is adjusted to Adeliver lubricating liquid from the reservoir 26 at a relatively rapid rate, so that there is-an excess of lubricant around theY advancing rubber mass. At thesame time, the fine stream of shaping liquid 38 is introduced by the pump 45throug-h line 48,r passageway' 49, and the hollow needle 39. 'Ihe rubber mass, surrounded lby lubricant and having a iine stream-38 `0f liquid deposited along its central axis, advances through the heated tube I1. When the leading end ofthe rubber has passed through the pinch rolls 54 and 55, the variable speed lubricant pump 21 is adjusted so as to introduce to the surface of the passing rubber only a very small amount of lubricant, suiicient to form a thin, continuous lubricating lm, having a thickness of, say, about .0008 inch.- The resistance to flow of rubber'fromthetube I1 created by the pinch rolls causes the rubber mass to fill up entirely the vulcanizing tube I1, displacing the excess lubricant which was introduced at the start of the process, and permitting substantially vulcanized in the time that it takes Y the stock to traverse vthe length ofthe die.

The stream of liquid 38 passes along 'with the advancing rubber to the exit end of the tube and through the pinch rolls Bland 55. The pressure exerted by the pinch rolls isV adjusted bymeans of the adjusting :screw 11"so that the flow of liquid from the interior of the rubber mass in the conning tube I1 is restricted, and' an enlarged liquid bubble 53 collects within` the plastic rubber mass I3. In this way the rubber is shaped, by hydraulic pressure, in the form ofy a tube 31 which becomes at least vpartially vulcanized before it leaves the confining tube I1'. Since'the vulcanization takes place underpressure, a dense homogeneous productis obtained.

The variable speed transmission 6| Ais adjusted, as mentioned previously, to drive the vpinch rolls- 54 and 55 at a rate corresponding to the desiredrate of withdrawal of rubber from the chamber I1, in order that the rubberA tube 31 will have thetdesired'wall thickness.

'Under steady operating conditions, ,typical hydraulic v'shaping V'pressures and 'lubricant' pressuresas registered on the.` gauges 31| and', may.be,for example, from 50V to 200 p.s.i. The huid ,used to shape the rubber maybe any suitable.V liquid or gasr not deleterious to theerubber compound, e. g. glycerine, water, steam,` nitrogen, silicone, mold release 1 fluids,V etc.

The coniining tube I1, instead of'. being round in cross-section, may have other desiredforms to produce articles` of different shapes.

Materials other than rubber may bel-employed in this process, such asthermoplastic resinsI having somewhat rubbery properties at room temperature. In this case ther confining chamber I1 may becooled' instead ofv heated,- and the thermoplastic material maybe introduced thereto lina heated, highly plastic sta-te;` The shaping'bubble 53 will form within the mass in the heated plastic state, and the thus shaped 4plastic will be cooled sufticiently to retain its shape -before emergingfrom the confining chamber.A

Thermosetting resins may be employed if desired, notably those which have sufficient elasticity after curing to undergo compression at the exit end of the confining chamber Without becoming permanently deformed.

The'invention-is particularly welladapted to the manufacture of vgum rubberarticles which have Ypreviously been manufactured by -relatively inconvenient and inefdcient processes involving wrapping of the shaped-gum rubber articlefwth cloth or theA like during vulcanization. Gum rubber tubing can be made Umore conveniently and economically by `this method and thev product has asuperiorappearance'to that .made` by conventional processes, being smoothY and glossy on its inner and outer surfaces. This is'of particular advantage in tubing for surgical use, since the smooth surfacesY facilitate cleaning and sterllizing the tubing.

From the foregoing description, itis evident that the process and apparatus of `.this invention a-re susceptible of-many modiiications,and afa. ford a-convenient means of-continuously manu-Y facturing a wide variety ofVv shaped articles hav'- inga hollow'interior. Because the articles are shaped under pressure. in a coniining chamber, dense, homogeneous products free fronrinternal defects; or discontinuities are obtained. The passage of the article through a lubricatedconfining, chamber while beingshaped 1resu-lts in products having smooth glossy surfaces,such as have heretofore beenobtainable onlyby,process..- ing short lengths of material in closed molds under pressure.

Having thus described my invention, what I claim andjdesire to protect by Letters-Patent-is:

'1. In amethod ofshaping continuouslengths ofarticles of rubbery material having anfannular, outer wallanda longitudiualcentral cavity, ,the steps of shaping the.y article byv extruding an initially shapeless mass of` the ymaterial in ai plastic state intov an elongated .shaping passage.. waythe plastic rubbery material'being maintained under -pressure within the nsaidv elongated shaping .passageway so that it tends to -fill vout the: entire. passageway as a solid mass in confining engagement.withthewalls of the passagewayj introducinga stream ofiiuidfnto the material within thepassageway, allowing the. stream.of. uid'toaccumulate to form a Vfiuid bubble within the material,V 4whereby. a longitudinal. centraly cavityl'ofthe desired sizeis createdinthe ma terlal' in the Vplastic state, yand 'thereafterl caus- 9 4 ing thematerial in the passageway to chang from a plastic state to a sufiiciently elastic state to regain its shape after deformation on emerging from the said passageway.

2. A method of extruding hollow articles of plastic material which comprises extruding a cylindrical mass of a plastic material and simultaneously confining a length of the material under pressure in a relatively soft, heated, plastic state so that it tends to form a solid cylindrical mass while so confined, inserting a quantity of liquid into the confined cylindrical mass to transform the mass into a tube by internal iiuid pressure, and causing the confined material to change from a soft, plastic state to a relatively elastic, shape-retaining state.

3. A method of extruding shaped plastic'articles having a longitudinal cavity comprising the steps of forcing an initially shapeless mass of the plastic material into and throughA an elongated conning chamber, the plastic material being maintained under back-pressure in the said confining chamber so that it tends to fill out the chamber entirely as a solid mass, introducing -a continuous, centrally longitudinal stream of fluid into the plastic material in the confining chamber, compressing the plastic material laterally as it passes from the confining chamber, so as to restrict the flow of said fluid from the chamber and thus cause a longitudinal bubble of the said uid to form within the plastic material, thereby creating a longitudinal cavity in the plastic material, and, concurrently with the passage of the plastic material through the confining chamber, curing the plastic material to change it progressively from a plastic state to a sufficiently elastic state to regain its shape after compression.

' 4. A method of continuously extruding rubber articles having a longitudinal cavity comprising the steps of forcing a stream of the rubber in the plastic state into and through an elongated confining passage, exerting pressure on the rubber in the plastic state Within the conning passage so that the rubber tends to fill out the confining passage entirely as a solid mass, introducing a continuous, centrally longitudinal stream of fiuid into the rubber in the confining passage, compressing the rubber as it passes from the confining passage to limitlthe iiow of said fluid from the confining passage, thus causing a longitudinal fiuid bubble to form Within the rubber in the plastic state and thereby shaping a longitudinal cavity in the rubber, and concurrently heating the rubber in the confining passage to effect vulcanization.

A method of shaping tube-like vulcanized rubber articles comprising the steps of passing an initially shapeless mass of rubber in the plastic state through an elongated confining tube, the said rubber in the plastic state being maintained under back-pressure within the said elongated conning tube so that it tends to fill out the tube entirely in close engagement with the walls of the tube as an essentially solid mass, iiowing a continuous stream of incompressible fiuid centrally into the rubber as it passes into the said tube, restricting the iiow of said inco1npressible fluid from the tube so that anenlarged body of said fluid accumulates Within the rubber in the plastic state, thereby converting the rubber mass into a desired tube-like form while it is still in the plastic state, introducing va film of liquid lubricant between the wall yof the confining tube and the outer surface ofthe passingl the rubber through an elongated rubber to prevent sticking thereof to the tube, and vulcanizing the rubber at least partially in the tube.

6. In an apparatus for making continuous lengths of articles having a hollow longitudinal cavity from extrudable material by forcing the material while in a plastic state through an elongated confining and shaping chamber, the combination which comprises an external die member for extruding a stream of the plastic material into said chamber, means for introducing a stream of uid into the material in the chamber, and means for restricting the f'low of said extrudable material and said fluid from the chamber to-cause the said stream of fluid to enlarge to form a fluid bubble in the material and to cause the material to fill out the confining and shaping chamber in pressurized engagement with the internal walls thereof, the pressure of the said bubble acting to form the desired longitudinal cavity in-the material in the plastic state. v

7. In an apparatus for making continuous lengths of articles having a hollow central axial cavity from plastic material by passing the material through an elongated die, the combination which comprises an external die member for 'extruding a stream of the plastic into said die,

means for owing a central longitudinal stream of iiuid into the passing material while in a plastic state, means for compressing the article as it passes from the exit opening of the die to limit the fiow of said fluid from the die and to limit the emergence of the plastic material from the die, thereby causingthe plastic material to fill out the die in pressurized engagement with the internal walls thereof, and thereby causing an accumulation of the said fluid which creates the desired cavity within the plastic material by fluid pressure, and means' for causing a change in the physical state of the plastic material in the die, at thelocation of said accumulation 0f uid, from a plastic state to a suiciently elastic state to regain its shape after said compression.

8. In an apparatus for extruding lengths of hollow rubber articles by vforcing the rubber throughA an elongated conning chamber, the combination which comprises an external die member for extruding a stream of the rubber into the said confining chamber, means for passing a stream of fluid into the rubber, in the chamber, means for restricting the flow of fluid from the chamber and for restricting the passage of rubber out of the chamber, therebf,7 causing the rubber to fill out the chamber under pressure and creating an accumulated body of fluid within the rubber which shapes the rubber in the chamber by fluid pressure, means for vulcanizing the rubber in the chamber, and means for introducing a film of lubricant between the wall of the chamber and surface of the passing rubber.

9. In an apparatus for extruding continuous lengths of tube-like rubber articles by forcing shaping passageway,the combination which comprises an external die member for extruding a stream of the rubber into said passageway, means -for passing a stream of iiuid into the rubber in the passageway, means for compressing the rubber article as it emerges from the passageway to restrict the flow of rubber and said fluid from the passageway, thereby causing the rubber to fill out the passageway in pressurized engagement with the 4walls thereof,l and causing a bubble of 11 thesaid fluid to form in the rubber toshape the rubber to a tube-like articlewhile it is in the plastic state, means for vulcanizing therubber in the passageway, and means for lubricating the outerA surface of therubber as it passes through the passageway.

-10. An apparatus for extruding rubber tubing and the like comprising an elongated shaping and confining chamber, an external die member for extruding a stream of the rubber into the chamber, means for forcing the rubber under pressure into and through the chamber inclose confining engagement with the interior walls rof the chamber, means for introducing a film of lubricant between the surface of the rubber and the walls of the chamber, means for introducing a central stream of iiuid into the rubber under pressure in the chamber, means for heating the chamber to vulcanize the rubber, and means for compressing the rubber after it emerges from the chamber to restrict the flow ofA said fluid therefrom and thereby form an accumulated bubble -of the said fluid within therubber, said bubble shaping the rubber in the chamber in the plastic state in the desired tube-like form by fluid pressure.

1l. An apparatus for extruding rubber tubing and the like comprising an elongatedY die extension tube, an external die member for extruding a stream of rubber into the dieextension tube, means for forcing rubber under pressure into and through the external die and die extension tube, means for lubricating the surface of the rubber asit Apasses ythrough the die, a central hollow needle extending intofthe entrance end of said die extension tube for introducing a small central stream of liquid into the passing rubber, means for heating the tube to vulcanize the rubber as itpasses through the tube, a pair of pinch rolls engaging the exit end of the die extension tube, said rolls acting to compress therubber at it passes from the die extension tube, thereby restricting the flow of rubber and of said liquid from the die extension tube and causing an enlarged bubble of said liquid to form within the rubber while confined under pressure in the plastic state within theftube, the hydraulic pressure of said liquid bubble acting to shape the plastic rubber in the desired tube-like form.

12. A method-of forming tubes from thermor setting elastic material, comprising the steps of continually advancing an initiallyv shapeless mass of the material in a plastic state under pressure into an elongated confining chamber having the cross-sectional size and shape of the desired tube, heating the advancing material in said chamber toa soft, readily, deformable state, introducing a continuous central longitudinal stream of fluid into the soft, plastic mass in the confining chamber, restricting the flow of said plastic mass from the confining chamber so that thepla'stic tends to -ll out the chamber entirely in engagement with the lwalls of theconning chamber, restricting the flow of said fluidfrom within the mass so that an enlarged body of said fluid 4fQ'rms'vvithin the plastic mass while it is ccnned inthe said chamber,` thereby creatinga longitudinal cavity within the advancing plasticinass so that a tubular shape is imparted thereto, introducing a thin nlm of lubricating liquid-betweenA the wall of the confining chamber and the surface of `the advancing plastic mass `in contact'therewith to prevent sticking ofthe plastic to -the wall of the chamber, continuingl said yhea-ting of theadvancing soft plasticmass'insaid tubularvform until-the plastic mass becomesl thermosetto a self-supporting but elastic state, so that it retains'its shape Auponiemerging from said confining chamber, and controlling the rate of emergence Aof the advancing thermoset plastic tube from the confining chamber. to regulate the Wall thickness of the'said tube.

13-.A method of extruding hollow artic-les of plastic material which comprises extrudinga cylin'dricalznass of the plastic material andsir-nultaneously confining -a length of the material under substantial pressure so that it tends vto form a'solid cylindrical mass, inserting a quantity of liquid into the-confined cylindrical mass .to transform the mass into a tubeby internalfluid pressure, while maintaining' the outside diameter of the mass constant, and then causing the conned material to change from a soft, plastic state to aV relatively elastic, shape-retaining state.

14. An apparatus-for extruding rubber tubing and the like comprising iii-combinationanA elongated shaping and` ccnning chamber of constant internal diameter', an external dieniember at'- the entrance-to said chamber dening a die passageway for extruding a solid stream-of thc rubber into the said chamber, means for forcing the rubber under pressure into and through the external die and the chamber under suchrpressure that the rubber tends to nil out the said chamber entirely as a solid mass, means for introducing a nim of lubricant between the surf-ace of the rubber and the walls of the chamber, means for introducing a central stream of' uid into the rubber in the chamber, nieansfor heating the chamber to vulcanize the rubber, and nieans for compressing the rubber after it emerges from the chamber to restrict the flow of fluid therefrom and thereby form an accumulated bubble of nuid within the rubber, said bubble shaping the rubber in the chamber in the plastic state'in the desired tube-like form by 'fluid'pr'essure- 15, A method of making vulcanized rubber tubing having a definite wall thickness, comprising in combination the steps ci' heating an initially shapeless mass of vulcanizable rubber stock to extruding temperature, forcibly extruding a stream of the heated rubber mass into and through'a greatly elongated tubular confining and shaping die, the rubber stock Within said die being forced into pressurized confining engagement with the interior wall of the said die throughout its length, continuously introducing a thin film `of lubricant between the surface of the stock` and the wall of the die to prevent frictional contact between the surface of the rubber stock and the wall of the die, heating the die so that the stock passing through the die is progressively further heated from the aforesaid extrusion temperature to vulcaniz'ing temperature, the relation between the rate of heating of the die, the speed of extrusion, and the length of the die, being such that the stock emerges from the die in a vulcanized condition, squeezing the vulcanized rubber stock as it emerges from the exit end of the die to create a definite resistance to flow of material out of the die and thereby developing a definite back-pressure in the material within the die, continuously introducing la fine stream of fluid at the center of the heated rubber stool; as it passes into the entrance to the rdie, the aforesaid lsqueezing action on the rubber at the exit end of the die causing the fine stream of fluid to becs-me enlarged forni a bubble of definite diameter within the rubber stock in the elongated die at a portion of the elongated die Where the heated rubber yin the softest condi- 13 tion, such softest condition occurring just prior to the time the rubber becomes vulcanized, Whereby the rubber stock becomes vulcanized in the form of a tube, the internal diameter of the tube being determined by the said diameter of the fluid r' bubble, and the external diameter of the tube being determined by the internal diameter of the elongated die.

MARK W. OLSON.

REFERENCES CITED The following references are of record in the file of this patent:

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